It is known in the art to provide a pickup truck having a cab portion for carrying passengers in a rear seat section behind the driver and a cargo box behind the cab portion for carrying cargo. It is also known to provide aligned openings in the cab portion and the cargo box for carrying longer loads which extend into the passenger compartment with the rear seat folded down. However, a need exists for providing a pickup truck or similar vehicle with a flexible panel and window system that is adapted to accommodate a variety of optional configurations for alternatively carrying a maximum passenger load or an extended cargo load under both covered and uncovered conditions where the cargo load is protected from or exposed to ambient external conditions.